Closed course testing to compare with humans would require about 800,000,000 miles of testing (10x length of average travel between fatalities). And that would just be for one version, every update would require that, and updates are about 100x internal version changes per year depending on how you count additional ML annealing.

That's about 80B test miles per year at about a capital cost of $0.50 per mile.

For a company that, say, spends ~10% on R&D, it would require the company be about a trillion dollars, which only Apple, etc. have reached.